The present invention relates to a motor-control apparatus which controls a synchronous motor (including a reluctance motor) and a vehicle using the motor-control apparatus, and especially to a motor-control apparatus suitable for an electrical car or a hybrid car.
Since information on the magnetic pole position of the rotor is necessary to control the rotational speed or the torque of a synchronous motor, the magnetic pole position is generally detected with a position-detection sensor such as an encoder, a resolver, etc. However, a position-detection sensor is expensive, and has a problem in that a short-circuit may occur in it under some using-environmental conditions. Therefore, magnetic pole position-detection methods in which a position-detection sensor is not used has been devised or developed.
For example, Japanese Patent Application Laid-Open Hei 8-205578 and Japanese Patent Application Laid-Open Hei 7-245981 disclose conventional magnetic-pole-detection techniques for a synchronous motor. Japanese Patent Application Laid-Open Hei 8-205578 discloses a method of detecting the saliency in a synchronous motor based on the correlation of the vector of voltage applied to the synchronous motor by means of a PWM control, and ripple components in motor current caused by the applied voltage. On the other hand, Japanese Patent Application Laid-Open Hei 7-245981 discloses a method of detecting the magnetic pole position of a synchronous motor by detecting parallel and orthogonal components in a current vector or a voltage vector, corresponding to an alternating voltage vector or an alternating current vector, applied to the synchronous motor with salient poles, calculating a phase difference angle between the flux axis and the applied vector based on at least one of the detected components, and determining the magnetic pole position based on the calculated phase difference angle.
The former method has an advantage that since ordinary PWM signals for controlling the voltage applied to the synchronous motor are used, an additional signal to detect the magnetic pole position is not necessary. And, the latter method has an advantage that since the magnetic pole position is detected by applying an alternating voltage or an alternating current to the synchronous motor, it is possible to detect the magnetic pole position, also during the stopping of the motor, in which the induced voltage useful for detecting the magnetic pole position is not available, or during the very low speed operation of the motor.
To implement the above former conventional technique, it is necessary to detect the motor current and voltage at every time the respective PWM signals change. That is, the motor current and voltage must be detected at least six times during one cycle of the carrier wave for PWM, and the correlation is calculated at each time of the detection, which in turn causes a problem in that a high-performance controller is needed. And, in the above latter conventional technique, it is necessary to apply the alternating voltage or current to the synchronous motor in order to detect the magnetic pole position, and this causes a problem in that the level of torque vibrations or noises increases in a high-load operation state.
An objective of the present invention is to provide a motor-control apparatus, in which any additional signal for detecting a magnetic pole position of a rotor in a motor is not necessary, and which is capable of detecting the magnetic pole positions without using a position-detection sensor while performing an ordinary PWM control, and which uses a low-priced digital calculation apparatus such as a microcomputer; and a vehicle using the motor-control apparatus.
The above objective is achieved by providing a synchronous motor-control apparatus including a synchronous motor, a PWM inverter for driving the synchronous motor, and a digital calculation apparatus for controlling the PWM inverter, the synchronous motor-control apparatus comprising: magnetic pole position-detection means, situated in the digital calculation apparatus, for obtaining the magnetic pole position based on current, which flows in the synchronous motor, input to the digital calculation apparatus; and control means for controlling the synchronous motor based on the detected magnetic pole position; wherein the magnetic pole position-detection means takes in the current, which flows in the synchronous motor, by operating an A/D converter with an interruption signal generated by the position-detection means in synchronization with PWM signals for driving the PWM inverter.
In the above magnetic pole position-detection means, it is necessary to determine a short-circuit state in the synchronous motor, and this short-circuit state is determined by examining whether the state of a PWM signal for each phase is in a high (Hi) state or a low (Low) state.
Further, if harmonic components of the rotation frequency of the synchronous motor are contained in the signals of the detected magnetic pole positions, it is desirable to locate a digital filter for removing the harmonic components at the output portion of the magnetic pole position-detection means, and to make its cut-off frequency changeable, corresponding to the rotation frequency of the synchronous motor.